Stimulated Brillouin scattering (SBS) generates Stokes signals having very low phase noise. This is desirable for ring laser gyroscopes, because reduction of signal phase noise increases rotation measurement accuracy. A ring may be circular, triangular or any other closed perimeter geometry.
Typically, two optical signals, from two corresponding lasers are injected respectively clockwise and counter clockwise into a waveguide resonator. Stimulated Brillouin scattering in the resonator generates, respectively counter clockwise and clockwise at least first order, or first, Stokes signals. The term Nth order Stokes signal and Nth Stokes signal are interchangeable; Nth can be first, second, etc.
However, the counter clockwise and clockwise first order Stokes signals are susceptible to coupling due to backscattering in the waveguide. As a result, the counter clockwise and clockwise first order Stokes signals may become mode locked, thus having the same frequency. As a result, the SBS ring laser gyroscope can no longer determine angular rotation. Therefore, there is a need to diminish or eliminate such mode locking effect.